The detection of the presence of a material and/or its amount in a particular environment becomes increasingly important in a society which seeks to monitor or manipulate its environment. Despite the long history of developing devices for measurement of various materials in liquid or other fluid media, there still remains ample opportunity for improvements in the sensitivity, efficiency, economy, and ease of use. Among such devices and measurement methods, various electrochemical devices and methods have shown potential for increased specificity and flexibility of measurement.
In one type of electrochemical device, the electrical signal of interest is due primarily to the interactions between the electrode surface and the solution of interest in a small region very near the electrode surface ("surface region"). In these devices, the portion of the solution ("bulk solution"), which is more than a short distance from the working electrode surface, does not contribute to and may interfere with the reactions and/or interactions of interest. One of the problems encountered in the use of such devices for measurement of analytes in fluid media, particularly biological media, is that the magnitude of the interaction of the components of the solution with the electrode and/or the effective rates of reactions in the solutions, as measured with the electrode, may be mediated and/or diminished by the interactions between the bulk solution and the surface region of solution. Such effects may arise by diffusion of surface-active species into the bulk solution and/or quenching of the surface reaction due to interaction with the bulk solution. For example, where the property to be measured is pH, the generally large buffering capacity of the bulk solution moderates the change in pH near the electrode surface, as well as the rate of change in pH, so that the magnitude of the observed electrode signal is substantially reduced and/or the effective responsiveness of the electrode to time-dependent processes is reduced.
To avoid such effects and to limit the solution to a volume which substantially completely interacts with the electrode over very short periods of time, it would be desirable to provide devices which allow for reactions of interest in relatively large volumes while measuring the result with a volume with which the electrode may effectively communicate. Such a feature would be preferentially selective of the reaction and/or interaction occurring between the solution and the electrode surface, and minimize interferences, damping effects, and the like between the surface region of the solution and the bulk solution.